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Comment by tasty_freeze | Hacker News Reader

That is the cartoon version. The raw stuff of evolution is variation and selection pressure. Mutations are an important long-term contributor to variation, but most variation isn't due to mutation. Eg, my two parents had five sons, and while there are some similarities, there are a lot of differences too. None of the variation was because of mutations.

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Sorry for the ELI5, but if the differences aren't due to [genetic] mutation, how do they get passed on to future generations?

I think the point is that variation is created by taking some material from the mother, and some from the father. A _mutation_ also creates variation, but refer to things like replications errors and "bit flips" due to, say, radiation.

But those aren't differences in the same way that mutations are. The chromosomes passed on by the grandmother are identical to those received by the granddaughter, unless you're talking about spilicing genes between chromosomes. The morphological differences in the daughter are from the genes being expressed differently in the context of her body and the father's DNA. (Or so 90's science class would have me believe.)

The daughter has some genes from the mother, and some from the father. Which genes are selected from which progenitor is random.

To have a big pool for recombinations, inbreeding is to be avoided and populations must be big enough.

My cryptological brain can't herp but replace here... The "selected at random" with "selected in ways we don't understand"

There are parts of the cell that are noise-based. I'm talking about quantum level noise so in many ways it's as random as it gets.

> Which genes are selected from which progenitor is random.

IIRC that's not completely true. In mammal females, there is competition at the chromosome level to determine which member of each pair will end up in the first polar body (which is discarded) and which one ends up in the secondary oocyte (which then splits up to become the ovum and the secondary polar body).

Each person has two chromosomes of each kind and they are mixed during the formation of the egg and sperms. For more details see https://en.wikipedia.org/wiki/Chromosomal_crossover

So, ignoring mutations, the next generation gets a never before seen chromosomes that are a puzzle of the chromosomes of the mother and another never before seen chromosomes that are a puzzle of the chromosomes of father.

I still can't find how common is the crossover, but in one link I got about 70 crossovers during the formation of the egg (with a lot of variations), that is approximately 3 crossovers per chromosome. I guess the crossover rate for the sperm is similar.

There is an exception with the X and Y chromosomes in males, that can't crossover, so the Y chromosome is inherited without crossovers, and it's much easier to track the male ancestor line in the Y chromosome. See https://en.wikipedia.org/wiki/Y-chromosomal_Adam

Think of the male RNA like an STD that the baby has inside its cell walls since... well, the beginning.

Like a virus that doesn’t need a penetration mechanism because it’s literally Trojan horsed into the egg.

A virus without a penetrator is basically like a cassette tape of DNA.

Derpy egg plays random cassette tape, baby’s DNA is... well the books are cooked as they say. Traits, emerge.

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